Ruthenium and ruthenium dioxide removal method and material

ABSTRACT

A method for removing at least a portion of a structure, such as a layer, film, or deposit, including ruthenium metal and/or ruthenium dioxide includes contacting the structure with a material including ceric ammonium nitrate. A material for removing ruthenium metal and amorphous ruthenium dioxide includes ceric ammonium nitrate and may be in the form of an aqueous solution including ceric ammonium nitrate and optionally, other solid or liquid solutes providing desired properties. In one application, the method and material may be utilized to etch, shape, or pattern layers or films of ruthenium metal and/or ruthenium dioxide in the fabrication of semiconductor systems and their elements, components, and devices, such as wires, electrical contacts, word lines, bit lines, interconnects, vias, electrodes, capacitors, transistors, diodes, and memory devices.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 09/990,480,filed Nov. 16, 2001, now abandoned, which is a divisional of U.S. patentapplication Ser. No. 09/675,635, filed Sep. 29, 2000, issued as U.S.Pat. No. 6,537,462 on Mar. 25, 2003, which is a continuation of U.S.patent application Ser. No. 09/146,365, filed Sep. 3, 1998, issued asU.S. Pat. No. 6,143,192, on Nov. 7, 2000.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION

The present invention relates to methods of and materials for etching,patterning, dissolving, or otherwise removing all or a portion of aruthenium-containing structure such as, for example, a layer, a film, ora deposit. The present invention more particularly relates to methods ofand materials for etching, patterning, dissolving, or otherwise removingat least a portion of a structure composed of ruthenium metal, rutheniumdioxide, or a combination of ruthenium metal and ruthenium dioxide,whether disposed on an object such as a substrate or otherwise.

The methods and materials of the present invention may be used inapplications wherein it is desirable to etch, pattern, dissolve, orotherwise remove all or a portion of a layer, film, deposit, or otherstructure composed of ruthenium metal, ruthenium dioxide, or acombination of ruthenium metal and ruthenium dioxide. Examples ofpossible applications of the present methods and materials include theremoval of waste deposits of ruthenium metal and ruthenium dioxide fromthe surfaces of tools, parts, components, and apparatuses employed inchemical vapor deposition, physical vapor deposition, and othertechniques using ruthenium metal and/or ruthenium dioxide. The presentinvention's methods and materials may be incorporated into, for example,planarization techniques such as chemical mechanical planarization, andalso may be utilized in, for example, the production of ruthenium masks,ruthenium-coated reflective mirrors, and catalytic ruthenium coatings,and in the fabrication of semiconductor systems and their elements,components, and devices, such as wires, electrical contacts, word lines,bit lines, interconnects, vias, electrodes, capacitors, transistors,diodes, and memory devices.

BACKGROUND OF THE INVENTION

Increasingly, ruthenium (Ru) metal is an important material insemiconductor device fabrication, and ruthenium layers, films, and otherstructures may be incorporated into semiconductor components andelements such as wires, electrical contacts, electrodes, capacitors,transistors, and diodes. Ruthenium also is used in many otherapplications and, for example, may be employed as building material formasks, as a coating on mirrors, to provide a surface for catalysis, ormay be applied to objects by chemical or physical vapor depositiontechniques so as to provide a surface coating having advantageous wearor corrosion properties.

One particularly advantageous application of ruthenium metal is its usein the formation of electrode layers in the fabrication of oxide highdielectric capacitors, wherein the ruthenium metal is typically appliedeither as a thin film by sputter deposition or as a conformal layer bymetal organic chemical vapor deposition. Ruthenium is a conductive metalthat oxidizes to form a similarly conductive ruthenium dioxide (RuO₂)layer on the surface of the existing ruthenium metal. Therefore, when anoxide high dielectric capacitor is formed, the surface of a rutheniumlayer provided as the electrode material will not form a secondarydielectric layer when oxidized to RuO₂ during the oxygen anneal of thehigh dielectric material. The fact that ruthenium's oxide form isconductive distinguishes it from other conductive metal film materialssuch as, for example, tungsten, tantalum, and titanium, all of whichform relatively non-conductive oxide layers. Certain other possiblecapacitor electrode materials do not oxidize during the application ofan oxidizing anneal to the high dielectric material. One such capacitorelectrode material is platinum. However, ruthenium provides advantagesover platinum when used as a capacitor electrode in that platinum has atendency to leak charge, a property that is not exhibited to the samedegree by ruthenium.

In fabricating semiconductor devices incorporating a ruthenium metalfilm, such as, for example, the above-described oxide high dielectriccapacitors, it may be necessary to etch, pattern, dissolve, or otherwiseremove at least a portion of the ruthenium metal film or its dioxide soas to provide a suitably configured electrode or other structure or tocompletely remove such a film as an aid in recovering improperly coateddevices. When ruthenium metal is provided on an object by chemical vapordeposition, physical vapor deposition, or other deposition techniques, afilm or other deposit ruthenium metal and/or ruthenium dioxide may bedeposited on surfaces of the tools, components, and apparatuses used inthe deposition process, and it may be desirable to remove the rutheniummetal and/or ruthenium dioxide therefrom.

However, both ruthenium metal and ruthenium dioxide are resistant toremoval by known wet etching techniques, and none of the wet etchantstraditionally used in semiconductor device processing, including aquaregia and piranha, will dissolve ruthenium. In fact, both the CRCHandbook and the Merck Index list ruthenium metal as being insoluble instrong acids and oxidizers and as being soluble only in molten alkalisalts, harsh etchants unsuitable for many applications, includingsemiconductor processing. Currently, if a layer or film of rutheniummetal or ruthenium dioxide must be etched or patterned in thefabrication of a semiconductor device, one of a number of dry etchprocedures is used, including oxidizing argon plasma and O₂ plasma etchprocedures. However, the use of any of those dry etch procedures toremove ruthenium metal or ruthenium dioxide results in the formation ofthe explosive compound ruthenium tetroxide (RuO₄). The rutheniumtetroxide must be removed or otherwise prevented from building todangerous levels during the dry etch procedures, and this may increasethe complexity and expense of such procedures.

Although ruthenium metal and ruthenium dioxide layers, films, and otherstructures are useful in semiconductor device fabrication, the use ofsuch structures in that application has been limited because of theinability to satisfactorily etch or pattern the structures using wetetch techniques and the distinct disadvantages resulting from use of dryetch techniques. For like reasons, it has heretofore been difficult toremove undesirable films, layers, deposits, or other structures ofruthenium metal and ruthenium dioxide from tools and other objects.Accordingly, a need exists for an improved method for etching,patterning, or otherwise removing at least a portion of a rutheniummetal or ruthenium dioxide structure.

BRIEF SUMMARY OF THE INVENTION

The present invention addresses the above-described deficiencies in theknown techniques and materials by providing a method for etching,patterning, dissolving, or otherwise removing all or a portion of afilm, layer, deposit, or other structure including ruthenium metaland/or ruthenium dioxide by contacting the structure with a materialincluding ammonium cerium (IV) nitrate, which also is known as cericammonium nitrate. The structure may be disposed on, for example, atleast a portion of a substrate or other object.

The present invention also provides a material that includes cericammonium nitrate and that may be utilized in the method of the inventionto remove all or a portion of a structure including ruthenium metaland/or ruthenium dioxide. According to one aspect of the invention, thematerial is an aqueous solution including ceric ammonium nitrate, andthe solution may include other components such as, for example,components that provide the solution with desired properties.

The material and method of the present invention do not result in theformation of the tetroxide form of ruthenium when used to etch, pattern,dissolve, or otherwise remove ruthenium metal and/or ruthenium dioxidefrom structures including those materials and provide an alternative toknown dry etch procedures for removing ruthenium metal and rutheniumdioxide from structures including those materials.

DETAILED DESCRIPTION OF THE INVENTION

As described herein, a method is provided for etching, patterning,dissolving, or otherwise removing all or a portion of a film, layer,deposit, or other structure composed of ruthenium metal and/or rutheniumdioxide. In the method, at least a portion of a structure comprisingruthenium and/or ruthenium dioxide (whether deposited on at least aportion of a substrate or an object, or otherwise provided) is removedby contacting at least a region of a surface of the structure with amaterial comprising ceric ammonium nitrate. The inventor has discoveredthat material comprising ceric ammonium nitrate will remove rutheniummetal or amorphous ruthenium dioxide without the formation of theexplosive tetroxide form of ruthenium.

Accordingly, the material of the invention for removing ruthenium metaland/or ruthenium dioxide includes an amount of ceric ammonium nitrate.The material of the invention may be, for example, a solution of cericammonium nitrate. The material may be in the form of a liquid etchantsolution, and, in one form, the solution may be an aqueous solutionwherein ceric ammonium nitrate and, optionally, other solutes, aredissolved in liquid water. Such other solutes may include, for example,acetic acid and other liquid or solid solutes such as agents forbuffering or enhancing dissolution of the ceric ammonium nitrate in thesolvent. Other additional components that may be added to the solutionwill be apparent to those having ordinary skill in the art. In one form,the material of the invention may include about 0.5 to about 70 weightpercent ceric ammonium nitrate. As used in the method of the presentinvention, the material of the present invention may be, for example, anaqueous solution including about 30 weight percent ceric ammoniumnitrate, about 10 weight percent acetic acid, and about 60 weightpercent water.

When the ceric ammonium nitrate material of the invention is applied asa liquid solution, it may be applied to the structure using any suitabletechnique for contacting a surface with a liquid, including immersionand spray techniques. The solution also may be applied to the surface asa component of a slurry. Once apprised of the details of the inventionas described herein, one of skill in the art will readily comprehendadditional methods for applying the material of the invention, whetherin liquid form or otherwise, to a structure. When applied by animmersion or similar technique, the immersion bath may be agitated inorder to enhance the contact of the ceric ammonium nitrate with theruthenium metal and/or ruthenium dioxide to be removed. The cericammonium nitrate material, whether a solution or otherwise, may beapplied to the ruthenium metal and/or ruthenium dioxide structure atroom temperature, if desired, and one manner of contacting at least asurface of the structure is to immerse at least a portion of thestructure in an aqueous ceric ammonium nitrate solution.

As used herein, the term “structure” refers to any monolithic mass of amaterial, including one or more layers, films, or deposits of anyconfiguration, including active or operable portions of a semiconductordevice. The term “substrate” as used herein refers to any thing on or inwhich a structure may be provided. For example, substrates includesilicon-based materials, such as silicon, silicon dioxide (SiO₂), andborophosphosilicate glass (BPSG), and also include other materials,including stainless steel, quartz, and insulators such as sapphire.Substrates also refer to one or more layers that may include all or aportion of a structure. When a structure is formed on a substrate, itmay be formed directly on the substrate or it may be formed on thesubstrate with one or more intermediate layers between it and thesubstrate. A substrate is often the lowest layer of material in a wafer.The present invention may be utilized with a doped silicon substrate, orwith other structures and technologies, such as silicon-on-insulator,silicon-on-sapphire, and thin film transistors.

According to one aspect of the invention, the method and material of theinvention may be applied to etch, shape, or pattern structures ofruthenium metal and/or ruthenium dioxide during the fabrication ofsemiconductor systems and their elements, components, and devices,including the fabrication of wires, electrical contacts, word lines, bitlines, interconnects, vias, electrodes, capacitors, transistors, diodes,and memory devices. The method and material of the present inventionalso may be used to etch, shape, or pattern ruthenium metal or rutheniumdioxide structures in other applications such as, for example,fabrication of ruthenium masks, ruthenium-coated reflective mirrors, andcatalytic ruthenium coatings. Because the present material may beapplied to a structure as a liquid solution and does not result in theformation of ruthenium's explosive tetroxide form, it provides anadvantageous alternative to existing ruthenium dry etch procedures.

The method and material of the invention also may be used to removewaste deposits of ruthenium metal and ruthenium dioxide from thesurfaces of tools, parts, components, and apparatuses employed inchemical vapor deposition, physical vapor deposition, and othertechniques for providing ruthenium metal and/or ruthenium dioxide on asubstrate or other object. As an example, after completing a chemicalvapor deposition process of coating ruthenium metal onto an object,ruthenium metal also may coat the several components of the depositionapparatus. Such components include the surfaces of the depositionchamber, the quartz susceptor window in the bottom of the depositionchamber, any plates or shields, and the shower head. As another example,after completion of a sputter process of coating ruthenium metal on anobject, the ruthenium metal may coat the sputter shields, collimator,sputter target, and deposition chamber. After either process, everythingbut the object that is to be coated must be cleaned and may be done soconveniently by the present invention. Accordingly, the presentinvention is directed to a method for removing a layer, film, coating,or other deposit of ruthenium metal or ruthenium dioxide from an objectincluding, for example, a tool, a part, a component, a window, a plate,a shield, a shower head, a collimator, or a chamber wall. In thatprocess, the object is contacted with the material of the inventionusing a technique such as, for example, a spray or immersion technique.

The ceric ammonium nitrate material of the present invention whether insolution form or otherwise, also may be used as an active chemicalcomponent of a slurry used in a planarization process for planarizing asurface. In such an application, the material of the invention isapplied to the surface and acts to remove ruthenium metal and/orruthenium dioxide from the surface that is planarized. The planarizationprocess may be a chemical mechanical planarization process, which mayinclude application of a frictional force, such as mechanical abrasion,to the slurry on the surface. Other parameters of the planarizationprocess may be readily determined by or will be apparent to those ofordinary skill.

Accordingly, the present invention also provides for a slurry for use inplanarization processes, including chemical mechanical planarization,and that includes an amount of ceric ammonium nitrate. The slurry formof the present invention provides selective application of the materialof the invention so as to restrict the region from which ruthenium metaland/or ruthenium dioxide is removed. The slurry may include, forexample, an amount of the material of the present invention in a formsuitable for incorporation into the slurry.

The present invention also is directed to a method for forming astructure on a substrate wherein ruthenium metal is provided on at leasta portion of a surface of the substrate and a portion of the rutheniummetal is removed therefrom by contacting at least a region of theruthenium metal with the material of the present invention, as describedabove and including, for example, applying the material by spray orimmersion techniques, so as to remove a portion of the ruthenium metal.The ruthenium metal may be provided on the substrate by any knowntechnique for providing ruthenium metal on a surface, including chemicalvapor deposition, physical vapor deposition, and sputter techniques, andmay form all or a portion of a device.

The present invention also encompasses a method for forming a structurewherein a layer of amorphous ruthenium dioxide is provided on asubstrate and the amorphous ruthenium dioxide is contacted with thematerial of the invention, as described above and including, forexample, applying the material by spray or immersion techniques, so asto remove a portion of the ruthenium dioxide. The amorphous rutheniumdioxide may be provided by any method known to those of ordinary skillin the art and may form all or a portion of a device.

In addition, the present invention includes a method for forming adevice wherein a first layer including ruthenium metal and/or rutheniumdioxide is provided on at least a portion of a substrate, and a portionof the first layer is subsequently removed by contacting at least aregion of the first layer with the ceric ammonium nitrate-containingmaterial of the invention, as described above. The device may be, forexample, a memory device, a capacitor, a transistor, a diode, a wire, anelectrical contact, a word line, a bit line, an interconnect, anelectrode, or a via. Subsequent to removal of a portion of the firstlayer by the present invention's material, a second layer of rutheniummetal and/or ruthenium dioxide, or of some other material, may beprovided adjacent to the first layer. The first and second layers may beprovided by any known method.

The present invention also is directed to a method for forming a devicewherein a first layer of ruthenium metal and/or ruthenium dioxide isprovided on at least a portion of a surface of a substrate, at least aportion of the ruthenium metal in the first layer is oxidized, and atleast a portion of the first layer is removed by contacting at least aregion of the first layer with the material of the present invention soas to remove ruthenium metal and/or ruthenium dioxide form the firstlayer. The first layer may be oxidized by any known means for oxidizingruthenium metal, including a rapid thermal anneal process.

A method for patterning a ruthenium metal structure also is provided andincludes contacting at least a region of a surface of a structure ofruthenium metal with the material of the invention, as described above.The method also may include the act of providing a mask on the rutheniummetal structure prior to contacting the surface of the structure withthe material of the invention. The method also may include the step ofremoving the mask subsequent to contacting the surface of the structurewith the material of the invention. The ruthenium metal structure andthe mask may be provided, and the mask may be removed, using techniquesknown to those of skill in the art.

As discussed above, one application of ruthenium metal is as theelectrode in a capacitor.

Accordingly, the present invention also includes a method for forming acapacitor wherein:

a first layer including ruthenium metal is provided on at least aportion of a substrate;

the first layer is etched using the ceric ammonium nitrate-containingmaterial of the present invention to provide a first electrode;

a second layer including ruthenium metal is provided on at least aportion of the substrate;

the second layer is etched using the ceric ammonium nitrate-containingmaterial of the invention to provide a second electrode; and

a dielectric is formed between the first and second electrodes.

In the foregoing method for forming a capacitor, the act of forming thedielectric may occur prior to the act of providing the second layer and,also, may include providing the dielectric on at least a region of asurface of the first electrode. More particularly, the act of formingthe dielectric may encompass providing a material on at least a regionof a surface of the first electrode and then oxidizing at least aportion of the material to provide the desired dielectric properties.

In a more basic form, the present invention includes a method forforming an electrode for a capacitor and wherein a layer of rutheniummetal is provided on at least a portion of a substrate, and the layer issubsequently patterned by applying the material of the invention to atleast a region of the layer.

The results achieved by use of the method of the present invention andby conventional etch methods on ruthenium metal films and rutheniumoxide films are provided in the examples below.

EXAMPLE 1

Samples of ruthenium metal deposited by chemical vapor deposition onSiO₂ were placed in baths of the following materials: aqua regia (3parts hydrochloric acid and 1 part nitric acid) at approximately 100°C.; piranha solution (a mixture of 1 part of a 50 weight % peroxideaqueous solution and 1 part of 98-99% sulfuric acid) at approximately100° C.; HCl/peroxide at approximately 85° C.; 85% phosphoric acidsolution at approximately 150° C.; ammonium hydroxide/peroxide (50/50 byweight) at approximately 100° C.; pure 100% liquid bromine at roomtemperature (approximately 20-25° C.); 10% by weight bromine (Br₂) inwater at approximately 20-25° C.; and KOH aqueous solution(approximately 30 weight % KOH at approximately 85° C.). Each of theforegoing materials were allowed to contact the ruthenium metal depositfor at least 30 minutes and in each case a detectable amount ofruthenium metal was not removed from the SiO₂ substrate.

The runs of Example 1 show that several know wet etching materials, aswell as other, harsher materials, will not remove ruthenium from a layerof that metal at a commercially significant rate.

EXAMPLE 2

Samples of ruthenium and ruthenium dioxide films on silicon, its thermaloxide (SiO₂), and borophosphosilicate glass (BPSG) were immersed in aroom temperature (approximately 20-25° C.) bath of CR-14 Chrome Etchantobtained from Cyantek Corporation, Fremont, Calif. The CR-14 ChromeEtchant consisted of 30% by weight ceric ammonium nitrate, 10% by weightacetic acid, and 60% by weight water and is commonly used for etchingchromium and chromium dioxide. The parameters and results of each runare provided below in Table 1. It will be seen that the CR-14 ChromeEtchant removed ruthenium metal from each of the three substrates. Theestimated ruthenium metal etch rates achieved were as high as 11.67Å/sec. (Ru on 8K thermal oxide) and as low as 2.63 Å/sec. (Ru on BPSG).The etchant also removed ruthenium dioxide from each of the threesubstrates if the ruthenium dioxide was deposited on the substrate in anamorphous form. No crystalline ruthenium dioxide was removed by theCR-14 Chrome Etchant.

TABLE 1 Film Deposition Method/ Characteristics of ApproximateDeposition Deposited Ru or RuO₂ Film Thickness Estimated Estimated EtchMaterial Temperature Film (Å) Etch Time Rate (Å/sec.) Comments Ru on SiCVD/200° C. crystalline 400   <2 min. 3.33 Ru film flaked offimmediately in etchant bath, but dissolved in etchant within 2 min. Ruon Si CVD/250° C. crystalline 1100   <2 min. 9.17 Ru film flaked offimmediately in etchant bath, but dissolved in etchant within 2 min. Ruon Si CVD/350° C. crystalline 320   30 sec. 10.67 Ru film etched offwithout flaking. Ru on 8K (8000 Å) CVD/200° C. crystalline 500  <30 min.thermal oxide (SiO₂) Ru on 8K CVD/200° C. crystalline 350  30 sec. 11.67Ru film flaked off immediately in thermal oxide (SiO₂) etchant bath, butdissolved within etchant within 30 sec. Ru on BPSG CVD/200° C.crystalline 790   <5 min. 2.63 Ru film flaked off immediately in etchantbath, but dissolved within etchant within 5 min. RuO₂ on Si CVD/150° C.amorphous 375   <1 min. 6.25 RuO₂ film did not flake. RuO₂ on SiCVD/150° C. amorphous 250   <4 min. 1.04 RuO₂ film did not flake. RuO₂on Si CVD/300° C. crystalline 125 no etch 0 RuO₂ film did not appear toetch within 30 min. RuO₂ on 8K CVD/150° C. amorphous 375 <1.5 min. 4.17RuO₂ film did not flake. thermal oxide (SiO₂) RuO₂ on BPSG CVD/150° C.amorphous 950   <1 min. 15.83 RuO₂ film did not flake. RuO₂ on BPSGCVD/300° C. crystalline <100 no etch 0 RuO₂ film did not appear to etchwithin 20 min.

EXAMPLE 3

Samples of ruthenium and ruthenium dioxide provided on siliconsubstrates were annealed using a rapid thermal process (RTP) in whichthe samples were quickly heated from room temperature to 750° C. andwere then immersed in a room temperature (20-25° C.) bath of the CR-14Chrome Etchant. The methods by which the ruthenium films were depositedon the substrates and then annealed are provided in Table 2. Table 2also provides the estimated times during which etching occurred and anestimated etch rate for each run. As was observed with the RuO₂ films inExample 2 that were not annealed, the annealed crystalline rutheniumdioxide film was not etched in the procedure.

TABLE 2 Film Deposition Method/ Characteristics of Approximate EstimatedDeposition Deposited Ru or RuO₂ Film Thickness Estimated Etch RateMaterial Temperature Film (Å) Anneal Procedure Etch Time (Å/sec.)Comments RuO₂ on Si CVD/150° C. amorphous 250 RT Pin N₂ @  4 min. 1.04 Aconductive RuO₂ layer existed 850° C. under the material etched away.for 30 sec. RuO₂ on Si CVD/300° C. crystalline 600 RT Pin O₂ @ no etch 0Film did not appear to be etched 850° C. within 10 min. for 30 sec. Ruon Si CVD/200° C. crystalline 400 RT Pin N₂ @ 10 min. 0.67 Film flakedoff immediately and 850° C. most of the flakes dissolved in the for 30sec. etchant in less than 10 min., but a residue remained at 10 min.

Accordingly, the present invention provides an improved method andmaterial for etching, patterning, dissolving, or otherwise removing atleast a portion of a structure including ruthenium metal and/orruthenium dioxide.

The present invention has been described in connection with certainembodiments thereof. Those of ordinary skill in the art will recognizethat many modifications and variations may be employed. All suchmodifications and variations are intended to be covered by the foregoingdescription and the following claims.

I claim:
 1. A method of removing ruthenium metal and ruthenium dioxide,the method comprising contacting a structure comprising at least one ofruthenium metal and ruthenium dioxide with a liquid etchant comprisingless than 30 weight percent ceric ammonium nitrate.
 2. The method ofclaim 1 wherein the liquid etchant further comprises greater than 0.5weight percent ceric ammonium filtrate.
 3. The method of claim 2 whereinthe liquid etchant is an aqueous solution.
 4. The method of claim 1wherein the liquid etchant further comprises acetic acid.
 5. The methodof claim 1 wherein the liquid etchant further comprises about 10 weightpercent acetic acid.
 6. A method of removing ruthenium metal andruthenium dioxide, the method comprising contacting a structurecomprising at least one of ruthenium metal and ruthenium dioxide with aliquid etchant comprising more than 30 weight percent ceric ammoniumnitrate.
 7. The method of claim 6 wherein the liquid etchant comprisesless than 70 weight percent ceric ammonium nitrate.
 8. The method ofclaim 7 wherein the liquid etchant is an aqueous solution.
 9. The methodof claim 6 wherein the liquid etchant further comprises acetic acid. 10.The method of claim 6 wherein the liquid etchant further comprises about10 weight percent acetic acid.